Method and apparatus for the complete, dry desulphurization of combustion waste gases comprising SO2 and dust

ABSTRACT

PCT No. PCT/EP91/01548 Sec. 371 Date Apr. 16, 1992 Sec. 102(e) Date Apr. 16, 1992 PCT Filed Aug. 14, 1991 PCT Pub. No. WO92/03211 PCT Pub. Date Mar. 5, 1992.Combustion waste gases of coal dust comprising SO2 and fly ash are completely and dry desulphurized by very quickly heating up the fly ash to a high temperature which, however, is below the sintering temperature of the fly ash, and cooling the combustion waste gases to a temperature, the distance of which to the water dew point is relatively small and is below 25 DEG  C. Thereby, SO2 is bound into the ash, so that the combustion waste gases become free of SO2. (FIG.

BACKGROUND OF THE INVENTION

The present invention refers to a method for the complete, drydesulphurization of combustion flue gases comprising SO₂ and particles,as well as to an apparatus for carrying out the method.

The method especially refers to the complete and dry desulphurization ofcombustion flue gases of the combustion of coal, in particular thecombustion of brown coal, in which fly ash is comprised in thecombustion flue gas.

The method further refers to the desulphurization of SO₂ containingcombustion flue gases of other combustibles which instead of fly ashcontain particles which have comparable properties described below.

Dry desulphurization means that the desulphurization process takes placeat such a temperature distance from the dew point of the combustion fluegases, that the equipment portions downstream of a combustor (dedustingequipment, chimney) can be operated without any occurrence ofcondensation.

For the complete desulphurization, only wet methods are known, in whichthe combustion flue gases are brought into contact with absorbingliquids, such as caustic potash solution. It is disadvantageous,however, that the combustion flue gases leave this step of the processcompletely or almost completely moistly saturated, which results incaking and corrosion of the downstream equipment portions, attemptsbeing then made to eliminate such results by re-heating the combustionflue gases.

Dry desulphurization methods are also known, in which for example CaCO₃is blown into the combustion chamber. It decays at approximately 900° C.to become CaO, which then partly reacts with SO₂ and SO₃. In thismanner, desulphurization degrees of slightly above 80% could be achievedbut not a complete desulphurization.

Desulphurization methods, in which the combustion flue gases togetherwith fly ash and/or added absorbentia are cooled down to almost the dewpoint of the combustion flue gases, or in which the dew point is raisedby adding water or steam, come closer to this object, see for example DE32 40 373 or DE 33 32 928. There, especially the last portion of thecooling process of the smoke gases is effected by previously addingother cooled-off fly ash and/or absorbentia to the combustion flue gas,to cool it further down thereby. Therein, it is desired to achieve thecooling-down to less than 5° C. above the dew point, since only thendesulphurization degrees of 90% and more could be achieved. A completedesulphurization by that method is not known up to now.

Another dry operating desulphurization method is described in themagazine ZKG 3/1990, pages 139-143. There, the SO₂ comprising combustionflue gases are passed through a fluid bed, which consists of Ca(OH)₂ andcement raw powder. The fluid bed is operated in close proximity of thedew point of water, especially at an operation temperature of about 65°C. with a dew point of between 58° and 61° C. Despite the high cost ofequipment, energy and absorbentia consumption, the desulphurization isonly achieved to a SO₂ contents of 423 mg/mn³. It is furtherdisadvantageous that the proximity to the dew point causes cakings, andthat the remaining SO₂ contents results in corrosions of the downstreamportions of the equipment. By means of a further decrease in thedistance to the dew point, which in this cases is only about 65°-61°=4°C., the desulphurization can be slightly improved, however the problemsconcerning caking and corrosion are increasing. A complete and drydesulphurization by means of this method is also impossible.

SUMMARY OF THE INVENTION

Complete and dry desulphurization , however, can be achieved by means ofthe method according to the present invention, which will now bedescribed with the aid of the example of desulphurization of thecombustion flue gases of the combustion of pulverized brown coal fromthe region of the river Rhine.

This combustible is known from literature. Its ash usually comprises 30to 50% Ca and Mg compounds, which in combustion calcinate to a largeextent to become CaO and MgO and which in the above manner bind SO₂ andSO₃. It is known, that by means of this method desulphurization degreesof 20 to 50% are already achieved. Comparable kinds of brown coal arefor example known from Saxonia, Hungary and countries outside Europe.The method according to the present invention can especially carried outvery easily with pulverized brown coal from these countries. This methodshall be described by means of the above example of the combustion ofpulverized brown coal dust from the region of the river Rhine.

The pulverized brown coal dust is burnt in a manner, that its heating-upspeed exceeds the critical value of 3000° C./sec and that it reaches atemperature of at least 900° C., preferably 1200° C. Thereby, allcomponents of the ash particles which are produced by the combustionwill be strongly surface-activated, which according to the heating speedlasts up to 10 sec and then slowly decreases. The higher the heatingspeed, the higher the surface activity. The best values are achieved atheating speeds of beyond 5000° C./sec. The ash particles have thehighest receptivity as soon as their temperature has exceeded 1200° C.,but have not become so hot that Fe₂ O₃ or impurities of the ash melt,which can easily be recognized when looking at the ash particles under amicroscope.

The flue gases of the combustion are then cooled down e.g. in a boilerin a known manner. Normally, the temperature is kept down at 130° C. to150° C. in consideration of the dedusting equipment, feed-watertemperatures and chimney.

According to the invention the flue gases are then further cooled downto a temperature distance from the water dew point of the combustionflue gases, which will be defined later, with the temperature distancedepending on how long the combustion flue gases and the fly ashparticles contained therein are kept at a temperature of less than 25°C. above the water dew point. With a residence time in this temperaturerange of 0.8-1.0 sec, the combustion flue gases have to be cooled downto less than 25° C. above dew point. The shorter the residence time inthe stated temperature range, the more the required distance from thedew point decreases to which the flue gases have to be cooled down. Incase of a residence time of 0.05-0.1 sec in the stated temperaturerange, the combustion flue gases have to be cooled down to a temperatureof 11° C. above the dew point, whereas intermediate values can beinterpolated linearly.

If the temperature difference from the dew point falls to less than 35°to 40° C., a fast bonding of the SO₂ takes place; SO₃, eventuallypresent, is already absorbed and does not play a role anymore. In casethe distance to the dew point is less than 10° to 25° C.--according tothe residence time in the previously mentioned temperature range--theSO₂ is quantitatively bounded. Thus, a complete desulphurization isachieved.

The beginning of the sulphur bonding can be recognized by the color ofthe combustion ash. This color is, typical for pulverized brown coalfrom the region of the river Rhine, normally yellowish or ocherish withvariations of brown. With the beginning of sulphur bonding, the ashbecomes green. If such a boiler, or a combustion flue gas cooler whichfollows such a boiler, is inspected, normally a light deposit of dust isfound on all surfaces. As long as this deposit still is yellowish,ocherish or brownish, no major bonding exceeding the previouslymentioned primary bonding of the SO₂ has taken place. The beginning ofthe SO₂ bonding can be recognized by the initial occurrence of greenash.

There, a certain amount of SO₂ is chemically bounded; the greenish colorof the ash points to an iron compound. If such ash is stored in a closedcontainer for a few hours and if this container is then opened, a light,typically pungent odor of SO₂ can be recognized. Obviously a purelyphysical surface absorption has additionally taken place, which willprobably slightly decrease in the course of time. After heating the ashup to 250° C. to 300° C., an exothermic reaction of the ash with theambient air under O₂ consumption takes place, and afterwards the ashacquires its known yellowish-ocherish-brownish color again. Also in thiscase a slight SO₂ odor can be recognized.

The influence of the residence time suggests, that in case of thebonding of the SO₂ the fine ash particles are especially effective. Thelonger the residence time, the higher the possibility for the bigger ashparticles to react.

The method according to the invention is also applicable for other SO₂comprising combustion flue gases, which do not comprise solidscomponents which can be compared to the components of the Rhine browncoal. To those, such fine grained solids could be added duringcombustion, while the requirements of surface activation according tothe invention must be fulfilled.

Principally, the method can be carried out with all devices of the priorart, which fulfill the requirements of the method. As an examplethereof, a device will now be described by means of which the conditionsof the method can be met with particular benefit.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained in detail with reference to theaccompanying drawings in which:

FIG. 1 is a schematic view of an installation for carrying out themethod of the invention;

FIG. 2 is a sectional side view of a burner used in the method of theinvention; and

FIG. 3 is a sectional side view of a burner of FIG. 2, a boiler heatedby the burner, and a cooler for cooling the flue gases leaving thevessel.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the scheme of the method. Combustion air as well as thepulverized coal entrained by the carrier air are supplied to the burner3 in a known manner. This burner heats the boiler 4. It can be effectiveto connect a cyclone separator 5 for oversized particles downstream tothe boiler 4. It is followed by a cooler 6, which is provided withinlets and outlets for the cooling medium. According to the invention,the cooling medium is adjusted in a known manner in a way that thecombustion flue gas facing surfaces of the heat transfer surface have atemperature between the dew point and the temperature below which theSO₂ is absorbed. The cooler 6 can especially be formed as a tube cooler,in which the combustion flue gases are flowing through the tubes whichare kept at the desired temperature by means of water cooling them fromthe outside. A fine dedusting device 7 follows the cooler 6 in a knownmanner, e.g. a cloth filter. The filtered combustion flue gases leavethe fine dedusting device 7 via the exhaust pipe 8.

The amounts of ashes leave the installation via the outlet devices 9aand 9b.

The tube volume of the cooler 6 exposed to the combustion flue gases,the connection tube 10 between the cooler 6 and the fine dedustingdevice 7 as well as the volume of the latter exposed to the particlescontaining gas determine the residence time of the combustion flue gasestogether with at least the finest particles of ash in the temperaturerange in which bonding of the SO₂ takes place. The residence time isdetermined in the known manner by the volume flow of the combustion fluegas and the above-mentioned volume.

It is in accordance with the prior art to maintain all surfacescontacted by combustion flue gases and ash at a temperature above thedew point of the combustion waste gas.

The presence of the cyclone dedusting device 5 is not essential for theprocess. It can be useful to separate eventually still burning oversizedparticles from the pulverized coal. Its separation capacity, however,has to be limited according to the known rules for cyclone dedustingdevices in a way that a sufficient amount of fine ash is present in itsoutlet. The sufficient amount of ash is defined by the fact that, whileall conditions of the process are fulfilled, with an insufficient amountof fine ash the bonding of the SO₂ is not complete anymore.

Important for the process is the achievement of a sufficiently highheating speed of the coal particles before and after the combustion. Therespective text books of the firing technology provide rules forachieving the desired heating speeds or residence times. Usually thesetext books do not talk about residence times but about combustionchamber loads. These are inversely proportional to the residence times.Combinations of high capacity burners and additional combustion chambersusually called combustors are especially suitable as long as thesedevices meet the practical demands of the pulverized coal combustion.This is preferably the case in the burner shown in FIG. 2. The principalstructure of the burner of the type shown in FIG. 2 is disclosed in U.S.Pat. No. 4,057,021 to Schoppe. The burner is supplied with combustionair 1 as well as coal dust entrained by the carrier air in a knownmanner. The flow of the combustion air 1 is homogenized in a collectorcompartment 12 and is then swirled in an inlet portion by means of aradial vane arrangement 13 disposed therein and having an axial lengthL1. Swirling, the combustion air 1 enters into a divergent combustionmuffle 17 having an inlet diameter D1 to which a downstream,water-cooled portion 18 adjoins, the combination of the combustionmuffle and of the water-cooled portion having an axial length L2. Aflame accelerating nozzle 19 having an axial length L3 and an outletdiameter D3 is connected with this water-cooler portion 18 downstreamthereof. An axially extending pulverized coal lance is inserted into thecombustion muffle, said coal dust lance having a reversing cap 21 at thefree end thereof and ending at the portion of largest diameter D2 of thewater-cooled portion 18 where the accelerator nozzle 19 is connected.

For a combustion capacity of 3.9 MW, the dimensions shown in thefollowing table are used according to the invention:

    ______________________________________                                                   D1 =   338 mm .0.                                                             D2 =   700 mm .0.                                                             D3 =   350 mm .0.                                                             L1 =   197 mm                                                                 L2 =  1470 mm                                                                 L3 =   850 mm                                                      ______________________________________                                    

The guide vanes 13 are preferably formed as a logarithmical spiral,having a spiral angle with respect to the circumferential directionbetween 6° and 12°, preferably 10°.

With these dimensions selected, a directed flow is obtained in thecombustion muffle, shown in FIG. 2, with only the downstream componentsbeing shown. These are superimposed by a circumferential component in away that a flow angle of about 45° with respect to the generating lineresults at the outer periphery.

In the selection of the stated dimensions, two groups of results areachieved:

a) Flame stability

A wall-near downstream flow extends from diameter D1 to diameter D2.There, about half of the flow amount turns radially inwardly and runsalong the lance 20 through the cross section of diameter D1 back to theregion of the guide vanes 13. Here, this flow turns radially outwardlyagain and flows towards the diameter D2 together with the fresh airdownstream. Between the throughput flow and the back flow a zone of veryintensive turbulence is formed, in which the flame stabilizes.

The pulverized coal 2 is injected with a preferably constant amount ofcarrier air and is blown into the back flow by the aid of the reversingcap 21.

Under the irradiation of the surrounding flame, the volatile componentsof the pulverized coal vaporize and form, together with the combustionair, a gaseous flame which together with the remaining pulverized coalburns out in a flame jet 22. Under the stated conditions, the jetattains a speed of about 100 m/sec, which is essential for keeping cleanthe combustion chamber connected downstream.

b) Emissions

The stated dimensions and operational data result in combustion flue gasemissions which are clearly below the limit of the TA Luft, a Germantechnical direction concerning the purity of emissions into air.

FIG. 3 shows a boiler which is suitable for carrying out the methodaccording to the invention, said boiler being a hot water boiler in thepresent case.

The boiler body 30 having the diameter D4 and the length L4 comprisesfire tube 31 having the diameter D5 and an inlet 32 for the cold backwater as well as an outlet 33 and an outlet 34 for the heated flowwater. Thereby, the water cooling of the combustion muffle shown in FIG.2 is ensured. This combustion muffle is arranged in the upper region ofthe front side of the fire tube 31 and blows its flame jet angularlydownwards onto the other end of the fire tube, in which in the lowerregion the inlets 36 into the first tube pass 37 are arranged.

Below the burner at least one blowing nozzle 35 is arranged, throughwhich up to 15% of the combustion throughput air can be blown into thefire tube, in order to support the combustion, as well as to blow awayash deposits. The blowing nozzle 35 can be combined with blowing devicesfor pressurized air or vapor, if impurities in the pulverized coal leadto deposits in the fire tube.

With the above measures one can keep the fire tube clean, which isadvantageous for the method of the invention, since in this waycontrollable temperature conditions are present. Deposits of ash or slagin the fire tube would disrupt the heat transfer and would alter thetemperature.

Since the combustion of pulverized coal continues into the first tubepass 37, it is advantageous to provide each individual tube of this tubepass with blowing nozzles, through which an additional amount of air 39of up to 15% of the amount of combustion air can be blown into the tubesof the tube pass 37. These air jets also keep the inlet regions of thefirst tube pass 37 clean.

For the stated boiler capacity of about 3.5 MW corresponding to thecombustion capacity of 3.9 MW, it is furthermore advantageous for themethod according to the invention to provide 25 tubes for the first tubepass, each tube having a diameter of 88.9×5 mm. This results insufficiently high speed to also avoid ash deposits in the tubes of thefirst tube pass 37 when operating at reduced load. On the other hand thespeeds are still not so high when operating in the upper load range ofthe boiler dynamic effects due to the combined effects of the gases inthe tubes with the elasticity of the gas volume in the fire tube 31would result. If the velocity of the combustion flue gases in the tubesof the first tube pass 37 is lower than a sufficiently high minimumvelocity, ash deposits would form in the tubes, which move like dunesthrough the tubes and lead to a pressure pulse each time they reach theend of the tube, which results in that a precise adjustment of theamount of combustion air will become difficult.

By means of the above-mentioned dimensioning of the tubes of the firsttube pass 37 only a limited cooling of the combustion flue gases toabout 500° C. is made with the result that the combustion reactionsstill taking place in the tube pass have sufficient time and temperaturelevel to complete. Ash properties resulting therefrom are advantageousfor the method of the invention.

In the front reversing chamber 40 the combustion flue gases cooled downto a temperature of about 500° C. are supplied to the tubes 42 of asecond tube pass, in which they are cooled down in the lower region ofthe boiler to temperatures of about 110° to 150° C. dependent on theboiler load and water temperature.

Considering the above-mentioned conditions, i.e. the ash transport onone hand and the avoidance of dynamical effects on the other hand, it isadvantageous for the method of the invention to provide 288 tubes in thesecond tube pass having each a diameter of 30×5 mm.

The cooled down combustion flue gases leaving the tubes 41 are suppliedto a flue gas exit tube 42. This tube is arranged in an advantageousmanner transversely to the axis of the boiler, with the combustion fluegases being supplied to the tube tangentially. In this manner it isachieved that throughout the entire length of the flue gas exit tube 42dead flow zones do not occur anywhere which could lead to ash deposits.

The arrangement with burner, fire tube, the individual tube passes andthe flue gas exit tube, shown entirely in FIG. 3, thus has aself-cleaning effect and keeps itself completely clean during operation.This is of great advantage for the method of the invention, sincethereby the entire ash is in the combustion flue gas and is of areproduceable configuration.

The device shown in FIG. 3 is also suitable with the same capacity andalmost the same efficiency also for the combustion of other pulverizedcombustibles, like e.g. pulverized hard coal, wood and the like and alsofor the combustion of liquid and gaseous combustibles.

For the application of the method of the invention for thedesulphurization of combustion flue gases of liquid fuels absorbients,e.g. pulverized limestone, must be blown into the combustion muffle inthe known manner, with the amount and processing depends on therespective rules of the prior art.

A remarkable property of the device shown in FIG. 3, especially in thecombustion muffle and the fire tube, is that the flow conditions thereindo not depend on the Reynolds number in the first approximation. Thatmeans, that in converting to other firing capacities the dimensions ofmuffle and fire tube have to be converted with the root of the capacityratio. It has to be considered, that burner systems according to FIG. 2do not have an upper capacity limit; however, such limit is given by theprocessing and reactivity of the respective combustible. With anincreasing capacity, higher flame speeds can thus be obtained in theknown manner, with the devices becoming somewhat smaller than wouldresult from the computation with the square root of the capacity ratio.This consideration corresponds to the prior art.

The first tube pass 37 and the second tube pass 41 are operating in theranges of the Reynolds numbers, in which the decrease in temperature isonly a function of the ratio of the length to the inner diameter of therespective tubes. If in conversion to other capacities the samecombustion flue gas temperature at the outlet of the boiler is to beobtained, the sum of the tube cross sections is converted correspondingto the capacity ratio in the known manner, with the sum of the ratios oftube length to the inner diameter remaining constant. Thus the dimensionand number of tubes of the respective tube pass are clearly definedaccording to the rules of the fluid technics. Further statements ondimensions therefor are not necessary.

If the device described in FIG. 3 should also fulfill the other limitsof the TA Luft, especially with respect to NO_(x) and CO, it is ofadvantage to select the following values for the diameter D5 of the firetube 31 and of its length L5:

    D5=1400 mm .0.

    L5=3850 mm.

Therefrom, a diameter of the boiler 30 of D4=2600 mm and a length of theboiler of L4=4100 mm results.

As mentioned in the beginning portion of this specification, the dewpoint may be raised by adding water or steam t the flue gases. In someinstances, it may be necessary in the method of the invention to raisethe dew point of the flue gases so as to establish a proper temperaturedifference from the dew point, as explained above. A preferred locationfor injecting water or steam into the flue gases is situated in the firetube 31 opposite to the burner, and may be performed by means of aninjector 43 arranged in the axis of the fire tube 31 and supplied via aninlet 44. It is preferred that the water or steam is finely dispersed byinjector 43 within the fire tube.

We claim:
 1. A method for the complete, dry desulphurization ofcombustion gases containing SO₂ and fly ash and resulting from thecombustion of pulverized coal and other combustibles containing ash,comprising the following steps:a) activation of the fly ash by heatingup the pulverized coal and any other combustibles containing the ashduring the combustion with a heating up speed of more than 3000° C./secup to a temperature of more than 900° C., but below the ash sinteringtemperature developing during a residence time within a flame, b)cooling the combustion flue gases to a temperature distant from thewater dew point, with the admissible highest value of the temperaturedistance being dependent on the residence time of the combustion fluegases between the termination of the cooling process and the time ofseperation of a fine grain portion of the ash, as follows:in case of aresidence time of 0.8 sec, the temperature distance is 25° C. maximum,in case of a residence time of 0.1 sec, the temperature distance is 11°C. maximum, and between the residence times of 0.8 and 0.1 sec, thetemperature distance is linearly interpolated between said maximums. 2.A method as set forth in claim 1, wherein the heating up speed is morethan 5000° C./sec.
 3. A method as set forth in claim 1 or 2, wherein thepulverized coal is heated up to a temperature of more than 1200° C.
 4. Amethod for the complete, dry desulphurization of combustion flue gasescontaining SO₂ and resulting from the combustion of combustibles whichdo not contain ash or whose ash amount is low wherein absorbentssuitable for the method are blown into a flame in pulverized form suchthat:a) absorbent particles are activated during the combustion processby heating up during the combustion with a heating up speed of more than3000° C. sec up to a temperature of more than 900° C., but below thesintering temperature developing during the residence time within of theabsorbents and the ash, respectively, within the flame, b) cooling thecombustion flue gases to a temperature distant from the water dew point,with the admissible highest value of the temperature distance beingdependent on the residence time of the combustion flue gases between thetermination of the cooling process and the time of seperation of thefinest grain portion of the particles, as follows:in case of a residencetime of 0.8 sec, the temperature distance is 25° C. maximum, in case ofa residence time of 0.1 sec, the temperature distance is 11° C. maximum,and between the residence times of 0.8 and 0.1 sec, the temperaturedistance is interpolated linearly between said maximums.
 5. A method asset forth in claim 4, wherein the particles are heated with a heating upspeed of more than 5000° C./sec.
 6. A method as set forth in claim 4,wherein the particles are heated up to a temperature of more than 1200°C.
 7. A method as set forth in claim 1 or 4, wherein a requiredundershooting of the admissible temperature distance to the water dewpoint is attained in that the combustion flue gases are cooled down tothe water dew point resulting from the combustion and the atmosphericalmoisture by contacting the gases with cooler surfaces.
 8. A method asset forth in claim 1 or 4, wherein water or steam is added to thecombustion flue gases to increase their dew point.
 9. A method as setforth in claim 1 or 4, wherein the combustion and the heating upeffected thereby of the particles of the combustion ash and of addedcombustibles, respectively, is carried out in a burner muffle, whichfires a heat receiving chamber.
 10. A method as set forth in claim 9,wherein the heat receiving chamber is a radiation compartment of aboiler.
 11. A method as set forth in claim 9, wherein the combustionflue gases flow through the heat receiving chamber and through flues ofa boiler and thereby cool down.
 12. A method as set forth in claim 10,wherein downstream of the boiler a cooler is connected which cools thecombustion flue gases at least to the said temperature distant to thewater dew point.
 13. A method as set forth in claim 12, wherein thecooler is operated in a way that the temperature of heat receivingsurfaces thereof exposed to flue gas of the combustion is higher thanthe water dew point of the combustion flue gases flowing therethrough.14. An apparatus for the combustion of pulverized coal and othercombustibles containing ash and for the desulpherization of combustiongases resulting from the combustion, comprising:a divergent burnermuffle having an inlet portion and a downstream convergent flameaccelerator nozzle, said burner muffle having, for a firing capacity of3.9 MW, the following dimensions:

    ______________________________________                                        diameter at the inlet of the muffle                                                                   D1 =     338 mm                                       diameter at the inlet of the accelerator nozzle                                                       D2 =     700 mm                                       diameter at the outlet of the accelerator                                                             D3 =     350 mm                                       nozzle                                                                        axial length of the inlet portion                                                                     L1 =     197 mm                                       axial length of the muffle                                                                            L2 =    1470 mm                                       ______________________________________                                    

with radial guide vanes being arranged upstream of the inlet whichsupply the combustion air at a spiral angle with respect to thecircumferential direction of 6° to 12°.
 15. An apparatus as set forth inclaim 14, wherein a fire tube is connected downstream to the burner,with said firing capacity of 3.9 MW said fire tube having the followingdimensions:diameter of the fire tube D5=1400 mm length of the fire tubeL5=3580 mm.
 16. An apparatus as set forth in claim 14, wherein arectangular firing chamber is connected downstream of the burner andhaving a length of 3580 mm and a hydraulic diameter of 1400 mm.
 17. Anapparatus as set forth in claim 14 or 15, wherein for the calculation ofthe apparatus dimensioned for firing capacities other than 3.9 MW theabove dimensions are calculated with the square root of the ratio of thefiring capacities, with the angle of the air guide vanes being keptconstant.
 18. An apparatus as set forth in claim 14 or 15, wherein at afront side of the flame nozzle below the burner at least one opening isdisposed, the blow-out cross-section thereof being dimensioned such thatthrough the opening up to 15% of the combustion air can be blown intothe flame nozzle, by means of which the combustion is supported anddeposited ash particles are blown away.
 19. An apparatus as set forth inclaim 14 or 15, wherein at a front side of the flame nozzle underneaththe burner a plurality of openings are provided through which steam orpressurized air can continuously or pulsatingly be blown into the flamenozzle for removal of deposits from the lower region of the flamenozzle.
 20. An apparatus as set forth in claim 14 or 15, wherein thecombustion flue gas outlets of the flame nozzle are located at the endthereof opposite the burner.
 21. An apparatus as set forth in claim 14or 15, wherein the combustion flue gas outlets of the flame nozzle areformed as openings in the lower regions of the flame nozzle which areconnected to the tubes of a downstream connected first tube pass.
 22. Anapparatus as set forth in claim 21, wherein blow-in openings areassigned to the tubes of the first tube pass, the cross-sections ofwhich are dimensioned such that up to 15% of the combustion air can beblown through the blow-in openings into the tubes of the first tubepass.
 23. An apparatus as set forth in claim 21, wherein with a firingcapacity of 3.9 MW the first tube pass consists of 25 tubes each havingthe cross-sectional dimensions of 88.5×5 mm.
 24. An apparatus as setforth in claim 21, comprising a second tube pass connected downstream ofthe first tube pass and consisting of 288 tubes each having thecross-section dimensions of 30×5 mm.
 25. An apparatus as set forth inclaim 24, wherein for firing capacities other than 3.9 MW the sum of thetube cross-sections of the tube passes is calculated proportional to thefiring capacity, in which for maintaining the combustion flue gastemperature at the boiler outlet the sum of the ratio of the tube lengthto their clear diameter is dept constant.
 26. An apparatus as set forthin claim 22 wherein with a firing capacity of 3.9 MW the first tube passconsists of 25 tubes each having the cross-sectional dimensions of88.5×5 mm.
 27. An apparatus as set forth in claim 22 comprising a secondtube pass connected downstream of the first tube pass and consisting of288 tubes each having the cross-section dimensions of 30×5 mm.
 28. Anapparatus as set forth in claim 27, wherein for firing capacities otherthan 3.9 MW the sum of the tube cross-sections of the tube passes iscalculated proportional to the firing capacity, in which for maintainingthe combustion flue gas temperature at the boiler outlet the sum of theratio of the tube length to their clear diameter is kept constant. 29.An apparatus as set forth in claim 14 or 15 wherein the guide vanes areformed in accordance with a logarithmical spiral.
 30. An apparatus asset forth in claim 14 or 15 wherein the spiral angle is from 8° to 10°.